Sensor units for sensing the angular position of a rotatable element often include induction sensors, for example known from U.S. Pat. No. 5,309,094, involving an encoder element, adapted to generate magnetic field variations, and a sensing element adapted to determine, on the basis of the magnetic field variations, the angular position of the rotating element. The data delivered by the sensing element are generally processed by electronic components integrated in a printed circuit board to which the sensing element is connected.
As this type of sensor unit is often used in assemblies including electrical motors, the sensing element and the printed circuit board are mounted in a shielding casing made of a metallic material, and adapted to protect the sensing element and the printed circuit board from too intense magnetic fields. As the shielding casing catches a substantially high portion of the magnetic fields that exist in its vicinity, it provokes electric potential differences between the shielding casing and the printed circuit board. These electric potential differences continuously increase and can reach a level at which electric arcs can occur and destroy some components of the printed circuit board.